In recent years considerable attention has been focused upon the development of polymers having high temperature resistance. Such polymers are useful, for instance, in the fabrication of textiles suitable for high temperature applications such as reentry parachutes for space vehicles, and applications where extreme non-flammability is desired.
Poly(bisbenzimidazobenzophenanthroline) when formed into fibers and films is recognized to be useful in the fabrication of extremely attractive products which are capable of withstanding highly elevated temperatures. Heretofore, poly(bisbenzimidazobenzophenanthroline) has been produced by a condensation reaction in a variety of polymerization media such as phosphoric acid (See U.S. Pat. Nos. 3,539,677 and 3,574,170), a molten Lewis acid solvent (See U.S. Pat. Nos. 3,798,201 and 3,864,310), and a sulfone (See commonly assigned U.S. Ser. No. 424,996, filed Dec. 14, 1973). Also, reference to the possible use of other organic solvents as a reaction medium has generally been alluded to in the literature.
Heretofore when phosphoric acid has served as the polymerization medium expensive tantalum reaction vessels commonly are required which are able to withstand the corrosive action of phosphoric acid at elevated temperatures. Recovery of dilute phosphoric acid generated in the process requires a substantial amount of energy and expense. In contrast reactions with molten Lewis acids can be done in glass vessels, however, when molten Lewis acids (e.g., antimony trichloride) have been utilized as the reaction medium, product recovery has proven to be tedious and unduly time consuming particularly when a larger than laboratory scale polymerization is attempted. For instance, a methylene chloride extraction of antimony trichloride has been found to be extremely slow if a high purity product is desired.
It is an object of the present invention to provide an improved overall process for the formation and recovery of poly(bisbenzimidazobenzophenanthroline).
It is an object of the present invention to provide an improved overall process for the formation of poly(bisbenzimidazobenzophenanthroline) employing an antimony trichloride polymerization medium wherein the product may be readily recovered.
It is another object of the present invention to provide an improved polymerization and recovery process for poly(bisbenzimidazobenzophenanthroline) employing a substantially closed loop system wherein the reaction medium and the precipitation medium effectively are conserved and recycled.
These and other objects, as well as the scope, nature, and utilization of the process of the present invention will be apparent to those skilled in the art from the following description and appended claims.